If you know that you need to file a tax return for the year ended 5 April 2018, and you have done nothing yet, then you need to tell the Revenue by 5 October 2018. If you have left it this long, then it would be best to see an accountant at once.

You need to file a tax return if you had income for the year ended 5 April 2018 that the Revenue don’t know about, or if you had any capital gains for the same year. Income usually comes from starting self-employment, but there are other possibilities.